The most familiar system for detecting the surface features of a terrestrial surface or object is the human eye. But there is far more electromagnetic information about an object than meets the eye. It is well known, for example, that all objects having a temperature above absolute zero emit electromagnetic radiation. Hot objects predominantly emit radiation at short wavelengths. Cool objects predominantly emit radiation at longer wavelengths. Objects also absorb and reflect incident electromagnetic radiation. The variation of an object's reflectance with respect to the wavelength of the incident light helps determine what an object looks like. Indeed, different materials and molecular structures emit and reflect electromagnetic energy in different but characteristic ways depending on the temperature of the material or the wavelength of the incident radiation.
There are a variety of commercially available sensors and imagers operable to detect various wavelengths and intensities of electromagnetic energy, both visible and invisible, and both reflected and emitted, emanating from various objects and materials. Employing knowledge about known characteristic energy absorption and radiation patterns for different surface and subsurface materials and molecular structures, it is possible to use information collected from such sensors and imagers to detect and identify surface and subsurface features of a place, region or object that are invisible to or hidden from the naked eye. These hidden or invisible features are commonly referred to as “anomalies.”
Surface and subsurface imaging technology has a wide field of applications. Imaging technology can and has been used, for example, to survey fields to search for pipeline leaks. In U.S. Pat. No. 4,963,742, I describe an airborne multispectral survey system comprising up to three infrared detectors and two video cameras. Using standard, commercially available video tape recorders, the system simultaneously captured and recorded images in both the visible region and in selected infrared bands of the electromagnetic spectrum of the terrain below. After the recording, analysis could be performed by simultaneously playing the infrared and video recordings to identify anomalies—areas where the infrared recordings detected temperatures outside of a given threshold and which could not readily be explained from the visible features of the terrain. That system, however, heavily on human observation and on-site inspection of anomalies. Moreover, given the limitations of the system, it was difficult to separate anomalies of interest from “false” anomalies (anomalies not of interest). Therefore, there is a need for more sophisticated multispectral remote sensing systems that facilitate improved anomaly analysis capabilities.